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https://issues.apache.org/jira/browse/LUCENE-2230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12832001#action_12832001
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Uwe Schindler edited comment on LUCENE-2230 at 2/10/10 2:22 PM:
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Hi Fuad,
thanks for submitting your changed FuzzyQuery. After quickly looking through
the classes I found the following problems:
- The cache is incorrectly synchronized: The cache is static but access is
synchronized against the instance.
- The cache is not limited, maybe it should be a WeakHashMap. It can easily
overflow the memory (as it consumes lots of memory).
- When you build the tree, you use a class from spellchecker:
org.apache.lucene.search.spell.LuceneDictionary. This adds an additional memory
consumption, esp. if the index has a large term dict. Why not simply iterate
over the IndexReaders's TermEnum?
- The cache cannot work correctly with per segment search (since 2.9) or
reopened IndexReaders, because it is only bound to the field name but not an
index reader. To have a correct cache, do it like FieldCache and use a combined
key from field name and IndexReader.getFieldCacheKey().
Else it looks like a good approach, but the memory consumption is immense for
large term dicts. We currently develop a DFA-based FuzzyQuery, which will be
provided, when the new flex branch gets out: LUCENE-2089
If you fix the problems in your classes, we can add this patch to contrib.
was (Author: thetaphi):
Hi Fuad,
thanks for submitting your changed FuzzyQuery. After quickly looking through
the classes I found the following problems:
- The cache is incorrectly synchronized: The cache is static but access is
synchronized against the instance.
- The cache is not limited, maybe it should be a WeakHashMap. It can easily
overflow the memory (as it consumes lots of memory).
- When you build the tree, you use a class from spellchecker:
org.apache.lucene.search.spell.LuceneDictionary. This adds an additional memory
consumption, esp. if the index has a large term dict. Why not simply iterate
over the IndexReaders's TermEnum?
- The cache cannot work correctly with per segment search (since 2.9) or
reopened IndexReaders, because it is only bound to the field name but not an
index reader. To have a correct cache, do it like FieldCache and use a combined
key from field name and IndexReader.getFieldCacheKey().
Else it looks like a good approach, but the memory consumption is immense for
large term dicts. We currently develop a DFA-based FuzzyQuery, which will be
provided, when the nex flex branch gets out: LUCENE-2089
If you fix the problems in your classes, we can add this patch to contrib.
> Lucene Fuzzy Search: BK-Tree can improve performance 3-20 times.
> ----------------------------------------------------------------
>
> Key: LUCENE-2230
> URL: https://issues.apache.org/jira/browse/LUCENE-2230
> Project: Lucene - Java
> Issue Type: Improvement
> Affects Versions: 3.0
> Environment: Lucene currently uses brute force full-terms scanner and
> calculates distance for each term. New BKTree structure improves performance
> in average 20 times when distance is 1, and 3 times when distance is 3. I
> tested with index size several millions docs, and 250,000 terms.
> New algo uses integer distances between objects.
> Reporter: Fuad Efendi
> Attachments: BKTree.java, Distance.java, DistanceImpl.java,
> FuzzyTermEnumNEW.java, FuzzyTermEnumNEW.java
>
> Original Estimate: 0.02h
> Remaining Estimate: 0.02h
>
> W. Burkhard and R. Keller. Some approaches to best-match file searching,
> CACM, 1973
> http://portal.acm.org/citation.cfm?doid=362003.362025
> I was inspired by
> http://blog.notdot.net/2007/4/Damn-Cool-Algorithms-Part-1-BK-Trees (Nick
> Johnson, Google).
> Additionally, simplified algorythm at
> http://www.catalysoft.com/articles/StrikeAMatch.html seems to be much more
> logically correct than Levenstein distance, and it is 3-5 times faster
> (isolated tests).
> Big list od distance implementations:
> http://www.dcs.shef.ac.uk/~sam/stringmetrics.htm
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